The local Costco here still requires you to insert a Costco card before you start pumping. It's around 5 cents/gallon cheaper than the next-cheapest gas.
I had my first taste of $4 hi-test last weekend in California--and I didn't like it. Cost me $56 to top up the tank in the M5, and I had more than a quarter-tank before topping up.
Motor oil is going through the roof, too. Try to find a quart of top-flight motor oil for less than $2.50. The M5 requires Castrol RS 10w60 full synthetic racing oil. Available only at BMW and Porsche dealers--at $9/liter.